Responses of units in the mesolimbic system to olfactory and somatosensory stimuli: modulation of sensory input by ventral tegmental stimulation.
It is well known that neurons of the nigrostriatal dopamine (DA) system respond to sensory stimuli, and our primary objective here was to ascertain if neurons in the terminal regions of the mesolimbic DA system respond to sensory input also. In addition, the effects of electrical stimulation of the ventral tegmentum, which contains the DA cells of origin of the mesolimbic system, on sensory-evoked responses in mesolimbic neurons was studied. In rats anesthetized with chloral hydrate, responses of single units to olfactory and somatosensory stimuli were recorded in 6 forebrain regions including nucleus accumbens and olfactory tubercle. Both increases and decreases in spontaneous firing rates were evoked in 225 of 336 units by one or more of the 8 types of sensory stimuli employed (5 olfactory, 3 somatosensory). Excitatory responses occurred twice as frequently as inhibitory responses, but a few units responded with excitatory responses to some stimuli and inhibitory responses to others. The proportions of units responsive to olfactory and/or somatosensory stimuli were different in different regions. After electrical stimulation of the ventral tegmentum, sensory-evoked responses were changed in 30 of the 49 units tested (61%). There were increases, decreases or combinations of a decrease followed by an increase in sensory-evoked responses, which persisted for 1-10 min after the application of a single electrical stimulus train. Haloperidol (0.3 mg/kg, i.p.) either blocked the effect of tegmental stimulation or decreased all responses. The present results demonstrated that units in the terminal regions of the mesolimbic DA system are responsive to sensory input and that these responses can be affected by prior electrical stimulation of the ventral tegmentum.
West
C H
CH
Department of Psychiatry, Emory University School of Medicine, Atlanta, GA 30306.
Michael
R P
RP
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D004558:Electric Stimulation; D006220:Haloperidol / Q000494:pharmacology; D008032:Limbic System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009833:Olfactory Pathways / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology*; D013268:Stimulation, Chemical; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology; D013681:Tegmentum Mesencephali / Q000187:drug effects / Q000502:physiology*
D006220:Haloperidol